just to clear up one point the code LMS XJ-HD166S is for a "Lite-on DVD Drive".
point two when you reset the BIOS to Defaults it will revert back to whatever the Manufacturer had set in your case the default is a floppy drive as first boot device.
It should not be required to keep reseting back to defaults unless there is a problem after the device list has been gathered, which should happen each time the PC is started.
if the hard drive is changed the details should show in the BIOS correctly otherwise the drive parameters will be faulty.
When you click F1 and go into the BIOS the first page, where you see the primary and secondary you, should show a "MAIN" use the arrow button here and if possible select the hard drive you have set as your system drive. if they do not show here go into the second windows and make sure of the boot up sequence 1st HD 2nd CD etc.
if not Please check that the Drive IDE flat cables are connected and pushed firmly into place in the motherboard ( there is a notch on one side of the flat connector which is complimentary to the socket )and the drives as well, and power molex plugs are firmly pushed in to the drives.
This link is to the HP/Compaq Web site for guides to how to refit a drive
http://h10025.www1.hp.com/ewfrf/wc/document?docname=bph03429&lc=en&cc=us&man_lang=en&dlc=en&product=307768&lang=enThis link is to the HP/Compaq Web site for few other guides
http://h10025.www1.hp.com/ewfrf/wc/documentIndex?lc=en&cc=us&docname=c00001661&man_lang=en&dlc=en&product=307768&lang=en& the pictures will amuse you i am sure
one question which may sound strange to you is the computer clock always good or is there some deviation in the time and you have to keep reseting it. there is a small battery on the motherboard about the size of a 10 pence piece if it is flat it can cause problems such as you are having there is a number on it either 2032 or 2035 usually 1.5 volts, they only last a few years at the most, they can be purchased at most electrical stores.